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Add support for wrapping asymmetric keys #41

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Add support for wrapping asymmetric keys #41

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baa9c22
Fix formatting of documentation
sosthene-nitrokey Dec 21, 2023
f21406e
Add tests for current serialization of PIN data
sosthene-nitrokey Dec 21, 2023
e3e02ee
Change key (de) serialization to allow using X25519 keys
sosthene-nitrokey Dec 21, 2023
f2bee12
Implement X25519 key generation
sosthene-nitrokey Dec 22, 2023
4918709
Implement deriving X25519 keys from pins
sosthene-nitrokey Dec 22, 2023
a73f23c
Use DecryptedKey abstraction
sosthene-nitrokey Jan 10, 2024
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3 changes: 3 additions & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ chacha20poly1305 = { version = "0.10.1", default-features = false, features = ["
hkdf = "0.12.3"
hmac = "0.12.1"
rand_core = "0.6.4"
salty = { version = "0.3.0", default-features = false }
serde = { version = "1", default-features = false }
serde-byte-array = "0.1.2"
sha2 = { version = "0.10.6", default-features = false }
Expand All @@ -24,7 +25,9 @@ trussed = { version = "0.1.0", features = ["serde-extensions"] }
[dev-dependencies]
quickcheck = { version = "1.0.3", default-features = false }
rand_core = { version = "0.6.4", default-features = false, features = ["getrandom"] }
serde_test = "1.0.176"
trussed = { version = "0.1.0", features = ["serde-extensions", "virt"] }
serde_cbor = { version = "0.11.2", features = ["std"] }

[patch.crates-io]
littlefs2 = { git = "https://github.com/Nitrokey/littlefs2", tag = "v0.3.2-nitrokey-2" }
Expand Down
43 changes: 25 additions & 18 deletions src/backend.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ use core::fmt;

use hkdf::Hkdf;
use rand_core::{CryptoRng, RngCore};
use salty::agreement::SecretKey;
use sha2::Sha256;
use trussed::{
backend::Backend,
Expand All @@ -25,9 +26,9 @@ use crate::{
extension::{reply, AuthExtension, AuthReply, AuthRequest},
BACKEND_DIR,
};
use data::{Key, PinData, Salt, KEY_LEN, SALT_LEN};
use data::{DeriveKey, PinData, Salt, CHACHA_KEY_LEN, SALT_LEN};

use self::data::delete_app_salt;
use self::data::{delete_app_salt, ChachaKey, DecryptedKey};

/// max accepted length for the hardware initial key material
pub const MAX_HW_KEY_LEN: usize = 64;
Expand Down Expand Up @@ -149,8 +150,8 @@ impl AuthBackend {
}
}

fn expand(kdf: &Hkdf<Sha256>, client_id: &PathBuf) -> Key {
let mut out = Key::default();
fn expand(kdf: &Hkdf<Sha256>, client_id: &PathBuf) -> ChachaKey {
let mut out = ChachaKey::default();
#[allow(clippy::expect_used)]
kdf.expand(client_id.as_ref().as_bytes(), &mut *out)
.expect("Out data is always valid");
Expand All @@ -162,7 +163,7 @@ impl AuthBackend {
client_id: PathBuf,
global_fs: &mut impl Filestore,
rng: &mut R,
) -> Result<Key, Error> {
) -> Result<ChachaKey, Error> {
Ok(match &self.hw_key {
HardwareKey::Extracted(okm) => Self::expand(okm, &client_id),
HardwareKey::Missing => return Err(Error::MissingHwKey),
Expand All @@ -183,7 +184,7 @@ impl AuthBackend {
global_fs: &mut impl Filestore,
ctx: &mut AuthContext,
rng: &mut R,
) -> Result<Key, Error> {
) -> Result<ChachaKey, Error> {
if let Some(app_key) = ctx.application_key {
return Ok(app_key);
}
Expand All @@ -197,7 +198,7 @@ impl AuthBackend {
/// Per-client context for [`AuthBackend`][]
#[derive(Default, Debug)]
pub struct AuthContext {
application_key: Option<Key>,
application_key: Option<ChachaKey>,
}

impl Backend for AuthBackend {
Expand Down Expand Up @@ -249,8 +250,8 @@ impl ExtensionImpl<AuthExtension> for AuthBackend {
let key_id = keystore.store_key(
Location::Volatile,
Secrecy::Secret,
Kind::Symmetric(KEY_LEN),
&*k,
k.kind(),
&k.data(),
)?;
Ok(reply::GetPinKey {
result: Some(key_id),
Expand All @@ -276,28 +277,34 @@ impl ExtensionImpl<AuthExtension> for AuthBackend {
Ok(reply::ChangePin { success }.into())
}
AuthRequest::SetPin(request) => {
let maybe_app_key = if request.derive_key {
Some(self.get_app_key(client_id, global_fs, ctx, rng)?)
} else {
None
let key_derivation = match request.derive_key {
Some(key_type) => Some(DeriveKey {
application_key: self.get_app_key(client_id, global_fs, ctx, rng)?,
key_type,
}),
None => None,
};
PinData::new(
request.id,
&request.pin,
request.retries,
rng,
maybe_app_key.as_ref(),
key_derivation,
)
.save(fs, self.location)?;
Ok(reply::SetPin.into())
}
AuthRequest::SetPinWithKey(request) => {
let app_key = self.get_app_key(client_id, global_fs, ctx, rng)?;
let key_to_wrap =
keystore.load_key(Secrecy::Secret, Some(Kind::Symmetric(32)), &request.key)?;
let key_to_wrap = (&*key_to_wrap.material)
let key_material = keystore.load_key(Secrecy::Secret, None, &request.key)?;
let material_32: [u8; 32] = (&*key_material.material)
.try_into()
.map_err(|_| Error::ReadFailed)?;
let key_to_wrap = match key_material.kind {
Kind::Symmetric(32) => DecryptedKey::Chacha20Poly1305(material_32.into()),
Kind::X255 => DecryptedKey::X25519(SecretKey::from_seed(&material_32)),
_ => return Err(Error::NotFound)?,
};
PinData::reset_with_key(
request.id,
&request.pin,
Expand Down Expand Up @@ -347,7 +354,7 @@ impl ExtensionImpl<AuthExtension> for AuthBackend {
let key_id = keystore.store_key(
Location::Volatile,
Secrecy::Secret,
Kind::Symmetric(KEY_LEN),
Kind::Symmetric(CHACHA_KEY_LEN),
&*key,
)?;
Ok(reply::GetApplicationKey { key: key_id }.into())
Expand Down
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